Elastic Launched Glider B

coachchuckaahs
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Re: Elastic Launched Glider B

Post by coachchuckaahs » February 24th, 2020, 9:36 am

NewSciolyer wrote:
February 22nd, 2020, 12:22 pm
Is it weird that for one of my gliders in order for it to transition well I have to bank in the opposite direction of the turn 40 degrees?
As others have noted, it is something non-symmetric about your plane. If it was 10-20 degrees bank, I would not worry too much. However, with 40 degrees opposite bank, something is way off.

Look first for something not statically symmetric. A wing twisted, uneven sanding, etc., as others have mentioned.

Then look for something dynamic. Measure your flap stiffness at several points along the span, on each side. They should agree. (We have balsa flaps, so uneven sanding or uneven grain in the wood can cause this). Carefully feel the twist stiffness of the leading edge area, both winds need to have similar stiffness. Carefully review the tip bending (outside the flaps). One typical method of trimming to eliminate bunting is to bend both tip TE's up a bit, which at high speed levers the whole wing to twist to more positive incidence. A little goes a long way. So if your left tip TE is up a little higher than the left wing, then at launch speeds the left wing is going to higher incidence and rolling the plane to the right. It seems backwards, but watch some of Josh's videos, he explains it nicely. It is possible you bent the left TE up to try to cancel right roll (thinking ailerons), but actually made it worse!

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Re: Elastic Launched Glider B

Post by NewSciolyer » February 24th, 2020, 2:29 pm

As others have noted, it is something non-symmetric about your plane. If it was 10-20 degrees bank, I would not worry too much. However, with 40 degrees opposite bank, something is way off.

Look first for something not statically symmetric. A wing twisted, uneven sanding, etc., as others have mentioned.

Then look for something dynamic. Measure your flap stiffness at several points along the span, on each side. They should agree. (We have balsa flaps, so uneven sanding or uneven grain in the wood can cause this). Carefully feel the twist stiffness of the leading edge area, both winds need to have similar stiffness. Carefully review the tip bending (outside the flaps). One typical method of trimming to eliminate bunting is to bend both tip TE's up a bit, which at high speed levers the whole wing to twist to more positive incidence. A little goes a long way. So if your left tip TE is up a little higher than the left wing, then at launch speeds the left wing is going to higher incidence and rolling the plane to the right. It seems backwards, but watch some of Josh's videos, he explains it nicely. It is possible you bent the left TE up to try to cancel right roll (thinking ailerons), but actually made it worse!
Yes, that was it! I didn't realize that you have to twist the entire wing. Once I cracked the wing a by twisting it and reglued it, problem was solved! Thanks!
Last edited by NewSciolyer on March 7th, 2020, 8:36 am, edited 1 time in total.

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Re: Elastic Launched Glider B

Post by NewSciolyer » March 7th, 2020, 8:36 am

Is it normal for a canard plane to "wobble" when tossed and even out? It kinda waves like a swingset for a few seconds and then evens out when tossed.

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Re: Elastic Launched Glider B

Post by builderguy135 » March 7th, 2020, 12:13 pm

NewSciolyer wrote:
March 7th, 2020, 8:36 am
Is it normal for a canard plane to "wobble" when tossed and even out? It kinda waves like a swingset for a few seconds and then evens out when tossed.
If one wing is heavier than the other, that could be an issue. Make sure both wings have the same weight and if you use flaps, make sure the flap deflections are equal.

However, the only thing that matters is your flight, not a practice toss. If it fixes itself during the transition, then it could be considered "normal".
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Re: Elastic Launched Glider B

Post by fifty_missions » March 7th, 2020, 3:28 pm

Let's look at the trim and fix options when a glider has a severe tendency to roll on launch. To begin with, any glider should be symmetric before test flying begins. To orbit and not hit the walls it will eventually have some magnitude of asymmetry. Next, speed has a changing effect on the glider''s flight. The fast launch speeds magnify the effect any slight trim differentiation. This means just a mm bend or twist that makes the glider fly smoothly in the glide may induce dramatic flight patterns on launch. For this exercise, our glider is a FLAPPER that rolls left on launch and barely shows any left orbit. Here are items to consider-

1) This glider shows that the right (starboard) wing is demonstrating higher lift. In most most long flying gliders, the glider is trimmed to fly into an orbit against the higher lift wing. This could as simple as slight right rudder. Note: The trailing edges of the fin and stabilizer should be sanded to about 1/64" thick to allow a pinch and bend the surfaces for more or less lift.

2) Another option is to create more lift on that left wing. The typical application is to lower the trailing edge except on a Flapper this may cause some sever drag and exacerbate the left roll. Instead, let's move to the front of the wing, the leading edge. This leading edge leads to be higher to create more lift. This can be done by two methods-
a) Rotate the left wing and twist it up. If it cracks, glue it such that the positive incidence stays.
b) Crack the leading edge at the root and move the leading higher by 2mm. Re-glue that wing at the root to keep that edge up. It may look funny but this is not a beauty contest.
c) Remove the wing, an reglue to the fuselage with the right wing rotated so that the left wing is slightly ahead.

3) Transition options-
a) For gliders that weigh 4 grams or more... use up elevator and ballast the nose to remove stall.... another option on the stall is to fly with a tighter orbit as this reduces the stall tendency
b) For gliders massing between 3.0 grams and 3.75 grams... remove some ballast from the nose but add down elevator. seems counterintuitive but this setup will help the glider fly "on-the-step" or slightly nose high without stalling.

4) There are instances of competitive gliders requiring a severe attitude and pitch angle on launch. It may feel awkward but if the glider is able to transition up high, try it!

5) Always start flight testing with a glider that stalls and not one that dives. Once the glider has proven to make a transition, proceed to trim out the stall.

6) Always assume the glider changes its aerodynamics from session to session. Trim as if a new glider with referring to past data for righthand or lefthand orbits. Gradually launch glider from horizontal to 45 degrees almost vertical if the glider can transition.

7) Always launch the glider with some degree of bank to induce an orbit.

Good Luck!

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Re: Elastic Launched Glider B

Post by MoMoney$$$;)0) » March 23rd, 2020, 10:42 am

Come on people we need to add to the best of 2020

Best of 2020

If you guys don't know how to add to the WIki, share me the photo privately, and I can add it on. :D
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